Organic light-emitting diode and method of fabricating the same

ABSTRACT

An organic light-emitting diode and method of fabricating the same. The organic light-emitting diode includes a substrate having a plurality of protrusions on a first plane thereof, a first electrode installed on a second plane of the substrate, wherein the second plane is opposed to the first plane, an organic light-emitting layer installed on the first electrode, and a second electrode installed on the organic light-emitting layer.

CROSS REFERENCE TO RELATED APPILCATIONS

This application is a Continuation of pending U.S. patent applicationSer. No. 10/883,102, filed Jul. 1, 2004 and entitled “OrganicLight-Emitting Diode”.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optoelectrical device, and morespecifically to an organic light-emitting display and a method offabricating the same.

2. Description of the Related Art

According to Snell's law n₁*sin θ₁=n₂*sin Θ₂ (wherein n₁ represents therefractive index of high-refractive materials, n₂ represents therefractive index of low-refractive materials, θ₁ represents the incidentangle of light, θ₂ represents the refractive angle of light), the totalreflection of light may happen when light is transmitted from higherrefractive index material to lower, for example, from glass ordielectric layer to the air. This is because the incident angle (θ₁) ofsome light in the higher refractive index (n₁) material is far enoughover a critical angle so as to create light having a 90° refractiveangle (θ₂), wherein some incident light cannot enter the lowerrefractive index (n₂) material.

For an organic light-emitting diode (OLED) featuring self-illumination,some inner light in a pixel cannot be emitted due to the totalreflection phenomenon, resulting in light consumption and reducedillumination efficiency. Additionally, when aluminum (Al) is used for acathode of an OLED, gray level or contrast may be reduced, owing toreflective light from the aluminum and glass plane in the presence ofexterior light. Currently, although a polarizer is used to reduce theexterior light effect, it may reduce the inner light transmittance,deteriorating illumination efficiency.

In the related art, an OLED structure is disclosed, for example, in U.S.Pat. No. 6,366,017, and in FIGS. 1. Referring to FIG. 1, a substrate 10is provided. An anode 12, an emissive layer 13, and a transparentconducting layer 14 are formed on the substrate 10 in order. After theemissive layer 13 produces light, some light passes through thetransparent conducting layer 14, and other remains, forming totalreflection, and resulting in the reduction of light transmittance, anddeterioration of element efficiency. To solve this problem, aDistributed Bragg Reflector (DBR) 15 is installed on the transparentconducting layer 14 in the related art to reduce total reflection,increasing element performance to obtain sufficient light source,improving brightness.

Nevertheless, DBR 15 may focus light at specific angles causing theexterior glare, deteriorating the quality of gray level or contrast, andfurther increasing the process cost.

SUMMARY OF THE INVENTION

In order to solve the conventional problems, an object of the inventionis to provide an OLED to reduce the total reflection and exterior glare,improving element performance thereof.

The OLED structure provided in the invention includes a substrate havinga plurality of protrusions on a first plane thereof, a first electrodeinstalled on a second plane of the substrate, wherein the second planeis opposed to the first plane, an organic light-emitting layer installedon the first electrode, and a second electrode installed on the organiclight-emitting layer.

The protrusions formed on the substrate in the present invention aredefined by photomask patterns, and may be arced, trapezoidal, orrectangular, and have proper sizes. Detailed characteristics of theprotrusions are described in the subsequent embodiments. Referring toFIG. 2, the protrusions 20 formed on the substrate surface can decreasethe incident angle 0, and refractive angle θ₂ to reduce the totalreflection of inner light, improving light transmittance. Additionally,after exterior light reaches the uneven protrusion surfaces, it presentsuniform scatter phenomenon to avoid exterior glare.

Another object of the invention is to provide a method of fabricating anOLED, including the following steps. A substrate is provided. Apatterned resist layer is formed on a first plane of the substrate.Subsequently, the substrate is defined to form a plurality ofprotrusions. A first electrode is then formed on a second plane of thesubstrate, wherein the second plane is opposed to the first plane. Next,an organic light-emitting layer is formed on the first electrode.Finally, a second electrode is formed on the organic light-emittinglayer.

The present invention provides another method of fabricating an OLED,including the following steps. A substrate is provided. A dielectriclayer is formed on a first plane of the substrate. Subsequently, thedielectric layer is defined to form a plurality of protrusions. A firstelectrode is then formed on a second plane of the substrate, wherein thesecond plane is opposed to the first plane. Next, an organiclight-emitting layer is formed on the first electrode. Finally, a secondelectrode is formed on the organic light-emitting layer.

In the present invention, the protrusions facilitating lighttransmittance are directly fabricated on the substrate. Compared to therelated art, requiring installation of an additional DBR, the inventionprovides a simpler and lower-cost process. In addition, the scattereffect of elements can be improved without extra fabrication process.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description and examples with references made to theaccompanying drawings, wherein:

FIGS. 1 is a cross section of an OLED in U.S. Pat. No. 6,366,017.

FIGS. 2 illustrates inner light passing through the uneven surface ofthe protrusion and the even surface of the substrate in an embodiment ofthe invention.

FIGS. 3 a-3 b are cross sections of the method of fabricating an OLED inthe first embodiment of the invention.

FIGS. 3 c-1 is a cross section of an OLED in the first embodiment of theinvention.

FIGS. 3 c-2 is a cross section of an OLED in the first embodiment of theinvention.

FIGS. 3 d is a cross section of an OLED in the first embodiment of theinvention.

FIGS. 4 a is a cross section of the method of fabricating an OLED in thesecond embodiment of the invention.

FIGS. 4 b-1 is a cross section of an OLED in the second embodiment ofthe invention.

FIGS. 4 b-2 is a cross section of an OLED in the second embodiment ofthe invention.

FIGS. 4 c is a cross section of an OLED in the second embodiment of theinvention.

FIGS. 5 illustrates scatter phenomenon of exterior light passing throughthe protrusion surface in an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

FIGS. 3 a-3 b are cross sections of the method of fabricating the OLEDaccording to the first embodiment of the invention. First, referring toFIG. 3 a, a substrate 300 is provided. The substrate 300 includes atransparent glass substrate or plastic substrate, wherein the plasticsubstrate is composed of polyethyleneterephthalate, polyester,polycarbonates, polyimide, arton, polyacrylates, or polystyrene.

Next, a patterned resist layer 305 with, for example, an arced crosssection, is formed on a first plane 3001 of the substrate 300, and othercross-sectional patterns are trapezoidal or rectangular, wherein arcedcross section is preferable. Subsequently, the substrate 300 is definedto form a plurality of protrusions 31 0 on the first plane 3001 thereofwith the patterned resist layer 305 used as an etching mask. Thepatterned resist layer 305 is then removed, as shown in FIG. 3 b.

Detailed characteristics of protrusions, such as size, shape, orfunction are described as follows. The height of the protrusions 310 isabout 4000˜8000 Å, preferably 6000 Å. The width of the protrusions 310is about 3000˜7000 Å, preferably 5000 Å. Cross-sections of theprotrusions 310 can be arced, trapezoidal, or rectangular (shown in FIG.3 d), preferably arced, wherein the contact angle between the arcedstructure and the substrate 300 is not greater than 90°, preferably 45°,the top of the trapezoidal is wider than the bottom thereof, or theopposite (shown in FIG. 3 c-1 and 3 c-2).

The protrusion 310 belongs to a microlens, and its refractive index isaltered with various substrate materials, preferably 1.3˜1.9. Thetransmittance of inner light is increased to about above 10% by therefractive lenses of the protrusions 310, improving scatter phenomenonof inner or exterior light at the protrusion surfaces simultaneously.Etching forming the protrusions 310 uses wet HF etching. Theconcentration of etching solution is about 2.5%. The etching temperatureis about 25° C. The etching time is about_(—)6˜10 min to control theexpected size, including the height and width of the protrusions 310.

Subsequently, a first electrode 320 is formed on a second plane 3002 ofthe substrate 300, wherein the second plane 3002 is opposed to the firstplane 3001. The first electrode is a transparent electrode, and maycomprise indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zincoxide (AZO), or zinc oxide (ZnO), preferably ITO.

Next, an organic light-emitting structural layer is formed on the firstelectrode 320, comprising an electron-transport layer (not shown), anorganic light-emitting layer 330, and a hole-transport layer (not shown)in order. The organic light-emitting layer 330 includes single ormultiple organic illuminative layers. The organic illuminative materialscomprise micromolecules or macromolecules of fluorescent orphosphorescent materials, wherein the micromolecule organic illuminativematerials covering the first electrode 320 are formed by vacuumevaporation, and the macromolecule organic illuminative materials areformed by spin-on, ejection, or screen printing.

Subsequently, a second electrode 340 is formed on the organiclight-emitting layer 330. The second electrode 340 includes atransparent, metallic, or complex electrode, wherein the complexelectrode is composed of multiple electrode layers, and the metalelectrode is Li, Mg, Ca, Al, Ag, In, Au, Ni, Pt, or combinationsthereof, further the complex electrode is Li, Mg, Ca, Al, Ag, In, Au,Ni, Pt, ITO, IZO, AZO, or ZnO.

Second Embodiment

FIGS. 4 a is a cross sections of the method of fabricating the OLEDaccording to the second embodiment of the invention. First, referring toFIG. 4 a, a substrate 400 is provided. The substrate 400 includes atransparent glass substrate or plastic substrate, wherein the plasticsubstrate is composed of polyethyleneterephthalate, polyester,polycarbonates, polyimide, arton, polyacrylates, or polystyrene.

Next, a dielectric layer 410 is formed on a first plane 4001 of thesubstrate 400. The dielectric layer 41 0 is a transparent material,comprising silicon oxide, silicon nitride, or silicon oxide nitride. Therefractive index of the dielectric layer 410 is altered with varioussubstrate materials, about 1.3˜1.9, preferably 1.5. The thickness of thedielectric layer 410 is about 4000˜8000 Å, preferably 6000 Å. Thedielectric layer 410 is formed by deposition, being a predeterminedregion of the subsequently formed protrusions.

Next, a patterned resist layer (not shown) is formed on the dielectriclayer 410. The cross-sectional patterns of the pattern resist layer maybe arced, trapezoidal, or rectangular, preferably arced. Subsequently,the dielectric layer 410 is defined to form a plurality of protrusions410 with the patterned resist layer used as an etching mask. Thepatterned resist layer is then removed.

Detailed characteristics of protrusions, such as size, shape, orfunction are described as follows. The height of the protrusions 410 isabout 4000˜8000 Å, preferably, 6000 Å. The width of the protrusions 410is about 3000˜7000 Å, preferably 5000 Å. Cross sections of theprotrusions 410 can be arced, trapezoidal, or rectangular (shown in FIG.4 c), preferably arced, wherein the contact angle between the arcedstructure and the substrate 400 is not greater than 90°, preferably 45°,the top of the trapezoidal is wider than the bottom thereof, or theopposite (shown in FIG. 4 b-1 and 4 b-2).

Protrusions 410 are microlenses. The transmittance of inner light isincreased to about above 10% by the refractive lenses of the protrusions410, improving scatter phenomenon of inner or exterior light at theprotrusion surfaces simultaneously. Etching forming the protrusions 410is performed by dry etching, such as inductively coupled plasma (ICP) orreactive ion etch (RIE).

The etching temperature is about 40° C. Etching pressure is about 5˜100mtorr. The etching time is about_(—)6 min to control the expected size,including the height and width of the protrusions 410, and the etchingpower is about 100˜1500 W.

Subsequently, a first electrode 420 is formed on a second plane 4002 ofthe substrate 400, wherein the second plane 4002 is opposed to the firstplane 4001. The first electrode 420 is a transparent electrode, and maycomprise indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zincoxide (AZO), or zinc oxide (ZnO), preferably ITO.

Next, an organic light-emitting structural layer is formed on the firstelectrode 420, comprising an electron-transport layer (not shown), anorganic light-emitting layer 430, and a hole-transport layer (not shown)in order. The organic light-emitting layer 430 includes single ormultiple organic illuminative layers. The organic illuminative materialscomprise micromolecules or macromolecules of fluorescent orphosphorescent materials, wherein the micromolecule organic illuminativematerials covering the first electrode 420 are formed by vacuumevaporation, and the macromolecule organic illuminative materials areformed by spin-on, ejection, or screen printing.

Subsequently, a second electrode 440 is formed on the organiclight-emitting layer 430. The second electrode 440 includes atransparent, metallic, or complex electrode, wherein the complexelectrode is composed of multiple electrode layers, and the metalelectrode is Li, Mg, Ca, Al, Ag, In, Au, Ni, Pt, or combinationsthereof, and further the complex electrode is Li, Mg, Ca, Al, Ag, In,Au, Ni, Pt, ITO, IZO, AZO, or ZnO.

Referring to FIG. 5 and, 3 or 4, the incident angle of inner light isdecreased to reduce the total reflection due to the protrusionstructures (310 or 410) of the substrate (300 or 400) when inner lightreaches the surfaces 50, improving illumination efficiency. Further, thescatter phenomenon 60 of exterior light reaching the surfaces 50 isformed, and exterior light passing through the substrate (300 or 400)have not been parallel light 70, as shown in FIG. 5, after reflectionfrom the cathode, and refraction from the surfaces 50 of the substrate(300 or 400), also producing scatter phenomenon to reduce glare.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1. An organic light-emitting diode, comprising: a substrate, having aplurality of arced protrusions on a first plane thereof; a firstelectrode, installed on a second plane of the substrate, wherein thesecond plane is opposed to the first plane; an organic light-emittinglayer, installed on the first electrode; and a second electrode,installed on the organic light-emitting layer.
 2. The organiclight-emitting diode as claimed in claim 1, wherein the height of theprotrusions is about 4000˜8000 Å.
 3. The organic light-emitting diode asclaimed in claim 1, wherein the width of the protrusions is about3000˜7000 Å.
 4. The organic light-emitting diode as claimed in claim 1,wherein the contact angle between the arced protrusion and the substrateis not greater than about 90°.